They're different.
The speed sensor is on the transmission and an ABS sensor is on each wheel hub. The ABS sensor does not affect the speedo, if you leave it unplugged the ABS will just not function.
Those 2 could be related if the car has an electrical problem.
I have a 2003 base 5 speed with ABS. On mine, there was no speed sensor on the transmission, the signal that drives the speedometer originates from the ABS module, I think it is an average of the four ABS sensors. One of the replacement transmissions I got from a junkyard did have a speed sensor, but I did not hook it up. I guess that tranny came from a car that did not have ABS.